Sometimes it is quite difficult to prove whether or not sex was consensual, so when a woman makes a false accusation of rape, she not only threatens the liberty and reputation of the accused, but the cases of future rape victims. If there is clear evidence the accusation is false, and no attempt was made to stop the state from acting on that false accusation, then the sentence should be of equivalent severity to the punishment for rape, because that's what harm the accusation does. To be clear, a rape victim should never be afraid of reporting the crime, so a punishment for the accuser should never be applied to cases with inconclusive evidence. Similarly, in order to minimize harm to the victim of a false accusation, someone that retracts a false accusation before it does significant harm shouldn't be punished nearly as severely as someone that makes a false accusation and fails to retract it.